This invention relates broadly to liquid treatment of hollow articles and, more particularly, pertains to improvements in the removal of liquid applied to inverted cans transported upon a conveyor belt moving through a can washing apparatus.
Newly formed metal food and beverage cans are typically cleaned of forming oils and other contaminants in a high volume can washer in which masses of upstanding or inverted cans are moved on a mesh conveyor between banks of water supply pipes or risers to each of which a plurality of particularly oriented spray nozzles are attached. By carefully controlling nozzle orientation, flow and pressure, the cans may be moved through the washer supported solely from below by the wire mesh conveyor belt on which the cans are carried.
In a typical can washer, as many as six separate liquid treatment stations are provided in serially connected orientation with the cans conveyed by the conveyor belt through, for example, pre-wash, acid cleaning, rinse, surface fixing, and two final rinse stations. Each station has its own underlying liquid collection tank and, to enhance recycling and prevent cross-contamination caused by the conveyor belt moving through multiple stations, it is desirable to remove as much liquid as possible from the cans and the belt as the cans move from one station to the next. Below the belt, a number of different devices may be used, including brushes which contact the underside of the belt or a vacuum stripper system which runs the full lateral width of the belt to extract excess liquid from the belt and the cans. In addition, compressed air blow-off units forming a blow-off system are positioned above the cans on the belt as they exit each treating station. The blow-off system blows free liquid out of the dished bottoms of the inverted cans and provides a flow of drying air.
The vacuum stripper system in the can washing system described above includes a vacuum tube sometimes provided with a pair of splitters which serve to distribute the vacuum applied to opposite ends of the tube so that the center of the tube receives a divided flow. In many instances, this flow modification proves to be insufficient such that the removal of excess liquid from the cans and belt by vacuum is less than desired. Because the conveyor belt is subjected to various substances, the excess liquid removed from the belt and the cans is often contaminated. Contaminated excess liquid evacuated from the vacuum stripper tube is generally collected at the ends of the tube and drained into a tank beneath the belt. However, because of the drainpipe structure extending between the vacuum stripper tube and the tank, contaminated air and liquid are frequently withdrawn back into the system in a manner which will impair the suction force applied to the vacuum stripper tube. In addition, the blow-off unit employed upstream of each treating station and the blower providing the suction force for the vacuum stripper tube are each driven by separate motors such that the intake of the blow-off unit is subject to handling contaminated air and the blower will blow an undesirable, contaminated mixture of excess liquid and air into a blower discharge pipe for return to the cans and the belt.
Accordingly, it is desirable to provide a system in which the vacuum induced flow which is split and travels through opposite ends of the vacuum stripper tube is better balanced so as to improve the amount of the excess liquid extracted from the cans and the belt. It is likewise desirable to provide a system having an excess liquid collection system which will prevent contaminated air and excess liquid from being withdrawn into the system in a manner which will not adversely affect the vacuum applied to the vacuum stripper tube. It is further desirable to provide a system in which the blower discharge pipe is connected to a separation device to remove any remaining contaminated excess liquid from the flow and direct a dry decontaminated air discharge into a return duct used to supply the blow-off system. It is further desirable to provide a system employing a single electric motor driven blower to supply the vacuum stripping flow and the compressed air for blow-off.